feat(FN-816): improve mobile UI theme, navigation, and changed-files viewer

- Fix modal entry flow, navigation, and reset behavior for mobile
- Apply mobile theme fixes and navigation improvements across dashboard
- Enhance ChangedFilesModal with mobile-friendly behavior and responsive layout
- Add comprehensive tests for ChangedFilesModal mobile interactions
- Fix orphaned pause path in executor and remove unused code
- Update dashboard README with mobile changed-files viewer documentation
- Add mobile-specific CSS styles for improved responsiveness
- Remove stale changeset for orphaned pause path fix

packages/dashboard/README.md

@@ -48,7 +48,7 @@ AI-guided interactive planning for creating well-specified tasks from high-level
 - **Layered Model Dropdowns**: Shared model combobox menus render in a top-level portal attached to `document.body`, so they stay above board columns and scrollable modal content instead of being clipped behind surrounding dashboard surfaces.
 - **Bulk Model Editing**: Update AI model configuration for multiple tasks at once in the list view. Select tasks via checkboxes (archived tasks excluded), then use the "Bulk Edit Models" toolbar to apply executor and/or validator model changes to all selected tasks. Selection persists in localStorage across page reloads.
 - **Task Details**: View full task specifications, agent logs, and attachments. The Agent Log tab expands to fill the full modal body height above the action bar, providing maximum vertical space for watching live agent output. The tab header shows the effective executor and validator model names resolved from task-level overrides or project/global settings fallbacks, matching the same resolution order the engine uses at runtime. The refinement modal positions the "Create Refinement Task" button adjacent to the feedback textarea alongside the character count, creating a tight input group that connects the submit action directly to the text being edited.
-- **Changed Files Viewer**: Click a task card's "files changed" button to open a dedicated diff viewer showing only files changed in that task worktree, with per-file statuses and sidebar navigation. On mobile (≤768px), the viewer switches to a single-pane flow: the file list and diff are shown one at a time with a back button for navigation between them. The board card file count and the changed-files viewer always agree — both use the same merge-base diff strategy, so the card never advertises files that the viewer cannot inspect
+- **Changed Files Viewer**: Click a task card's "files changed" button to open a dedicated diff viewer showing only files changed in that task worktree, with per-file statuses and sidebar navigation. On mobile (≤768px), the viewer switches to a single-pane flow: the file list and diff are shown one at a time with a back button for navigation between them. The viewer always opens to the file list on mobile, and only switches to the diff view when the user taps a specific file. Pressing Escape on the diff view returns to the file list first; pressing Escape again closes the modal. Loading, error, and empty states use theme-aware styling (including light mode). Diff syntax highlighting (additions, deletions, hunks) adapts to the active theme for correct contrast. The board card file count and the changed-files viewer always agree — both use the same merge-base diff strategy, so the card never advertises files that the viewer cannot inspect
 - **GitHub Import**: Import issues directly from GitHub repositories
 - **PR Management**: Create, monitor, and merge pull requests for in-review tasks
 - **Deep Links**: Dashboard task links using `?task=FN-123` (or `?project=proj_456&task=FN-123` for cross-project) open the task detail modal as a one-time launch. Dismissing the modal removes the `task` parameter from the URL so that refreshing the page does not reopen it. Other query parameters (e.g., `?project=...`) are preserved. Task detail modals opened normally from the board, list, or activity log are not affected.